Multilevel energy storage converter sub-module and capacitor voltage estimation method thereof

Abstract

The application discloses a multi-level energy storage converter submodule and a capacitor voltage estimation method thereof, and the method steps are as follows: S1, the junction temperature of the power device in each submodule, the shell temperature, the current, and the switching signal of each bridge arm are monitored in real time; S2, the power loss of each power device in the submodule is obtained by using the monitored junction temperature of the power device in the submodule, the shell temperature, and the thermal resistance parameters of the IGBT and the thermal resistance parameters of the diode in the power device data manual; S3, the conduction loss and the switching frequency of each power device are calculated; the switching loss energy of the power device in the submodule is obtained by using the monitored current of each bridge arm, the switching signal, and the device switching loss characteristic curve; and S4, the capacitor voltage in each submodule is obtained by using the power loss, the switching frequency, the switching loss energy, and the test voltage of each power device. The capacitor voltage estimation of the modular multi-level energy storage converter submodule is realized without increasing the hardware and software implementation cost.

Description

Technical Field

[0001] This invention belongs to the technical field of energy storage converters, and particularly relates to a multilevel energy storage converter submodule and its capacitor voltage estimation method. Background Technology

[0002] With climate change, environmental degradation, and energy shortages, renewable energy generation has garnered attention from both academia and industry. However, renewable energy generation is characterized by intermittency and randomness; therefore, its grid connection can impact grid security, stability, and power quality on the converter output side. Combining energy storage with renewable energy grid connection is an effective measure to stabilize renewable energy output and reduce its impact on the grid, thus mitigating the intermittency and randomness of renewable energy generation.

[0003] Modular multilevel converters adopt a modular structure. They are widely used in energy storage converters because they have advantages such as adjustable number of modules, flexible voltage and power level, high output power quality, reduced switching losses, and high redundancy and fault tolerance.

[0004] The bridge arm of a modular multilevel converter contains multiple sub-modules. Since capacitor voltage balancing of each sub-module within the bridge arm is necessary, the capacitor voltage values ​​of the sub-modules are required. Therefore, obtaining the sub-module capacitor voltages of the modular multilevel energy storage converter based on the junction temperature value from the temperature detection system is crucial for the reliable operation of the multilevel energy storage converter.

[0005] To address the issue of measuring the capacitor voltage of submodules in modular multilevel energy storage converters, conventional methods include installing capacitor voltage measurement sensors on each submodule, estimating the voltage using a Kalman filter algorithm, or employing an improved topology for voltage measurement. However, these methods increase the hardware cost of the modular multilevel converter, increase the complexity of software implementation, and reduce the applicability of the topology, thus limiting their practical application. Summary of the Invention

[0006] To address the issue of not increasing the hardware cost of modular multilevel converters and without increasing software implementation complexity, this invention proposes a multilevel energy storage converter submodule and its capacitor voltage estimation method, as detailed below:

[0007] A multilevel energy storage converter submodule, wherein the multilevel energy storage converter includes six bridge arms, each bridge arm including n submodules SM with the same topology connected in series, a bridge arm inductor Ls, and a bridge arm resistor R;

[0008] Submodule SM is a half-bridge structure, consisting of two diodes D1 and D2, two IGBT power switches T1 and T2, and a DC capacitor Ci. Diodes D1 and D2 are connected in reverse parallel to the switching terminals of IGBT power switches T1 and T2, respectively. The controlled terminals of IGBT power switches T1 and T2 are connected to signal S. j_k_i The input signal i at the series connection point of IGBT power switches T1 and T2 jk The two external terminals are connected via capacitor Ci.

[0009] Specifically, it includes the following steps:

[0010] S1. Real-time monitoring of the junction temperature T of power devices in each submodule. jun_j_k_i_g Where j = a, b, c; k = u, l; i = 1, 2, ..., n; g = T1, D1, T2, D2, and the shell temperature T of each submodule within the bridge arm. h_j_k_i The current i in each bridge arm jk Switching signals S of submodules within each bridge arm j_k_i a, b, c are the connection points of the three phases, and u, l are the upper and lower bridge arms of the multi-level energy storage converter, respectively.

[0011] S2. Utilize the monitored junction temperature T of the power devices in the submodule. jun_j_k_i_g , Submodule's shell temperature T h_j_k_i The thermal resistance parameter R of the IGBT in the power device datasheet th_jh_T The thermal resistance parameter R of the diode th_jh_D Obtain the power loss P of the power devices in the submodule loss_j_k_i_g ;

[0012] S3. Utilize the monitored current i of each bridge arm jk The switching signals S of the submodules within each bridge arm j_k_i The on-state voltage drop V of the IGBT in the power device datasheet ce0 Diode forward voltage drop V d0 IGBT on-state resistance R ce Diode on-resistance R d The conduction loss P of each power device in the submodule is obtained. con_j_k_i_g and switching frequency f sw_g ;

[0013] Using the monitored current i of each bridge arm jk The switching signals S of the submodules within each bridge arm j_k_i The switching loss energy E of the power devices in each submodule is obtained by comparing the switching loss characteristic curves of the power devices in the datasheets of each bridge arm submodule. sw_j_k_i_g ;

[0014] S4. Utilize the power loss P of each power device loss_j_k_i_g The switching frequency f of each power device sw_g Switching loss energy E of each power device sw_j_k_i_g The test voltage V in the power device datasheet ref_test Finally, the capacitor voltage V in each submodule is obtained. sm_j_k_i .

[0015] Specifically, step S2 includes: including the power loss P of IGBT 1. loss_j_k_i_T1 Power loss P of diode #1 loss_j_k_i_D1 Power loss P of IGBT No. 2 loss_j_k_i_T2 and the power loss P of diode 1 loss_j_k_i_D2 The calculation formula is as follows:

[0016]

[0017] In the formula T jun_j_k_i_T1 T jun_j_k_i_D1 T jun_j_k_i_T2 T jun_j_k_i_T2 This refers to the junction temperature of IGBT 1, diode 1, IGBT 2, and diode 2 in the submodule.

[0018] Specifically, in step S3, the switching frequency f sw_g The calculation steps are as follows:

[0019] Specifically, this includes the switching frequency f of IGBT No. 1 in the submodule. sw_T1 The switching frequency f of diode #1 sw_D1 The switching frequency f of IGBT No. 2 sw_T2 and the switching frequency f of diode #2 sw_D1 The calculation formula is as follows:

[0020]

[0021] In the formula, T is the fundamental frequency period of the converter operation.

[0022] Specifically, the switching loss energy E of the power devices in the submodule sw_j_k_i_g Specifically, this includes the energy loss E of the No. 1 IGBT switch. sw_j_k_i_T1 Energy loss E of diode #1 sw_j_k_i_D1 Energy loss E of IGBT No. 2 sw_j_k_i_T2 And the switching loss energy E of diode No. 2 sw_j_k_i_D2 The calculation formula is:

[0023]

[0024] In the formula p sw_j_k_i_T1 psw_j_k_i_D1 p sw_j_k_i_T2 p sw_j_k_i_D2 These represent the instantaneous switching energy of IGBT 1, diode 1, IGBT 2, and diode 2, respectively.

[0025] Specifically, in step S4, the capacitor voltage V in each sub-module sm_j_k_i The calculation method is as follows:

[0026]

[0027] In the formula V sm_j_k_i_0 V sm_j_k_i_1 V sm_j_k_i_2 V sm_j_k_i_3 These are the values ​​of the submodule capacitor voltage at time 0, T / 4, 2T / 4, and 3T / 4 of the fundamental period, respectively; P con_j_k_i_T1 P con_j_k_i_D1 P con_j_k_i_T2 P con_j_k_i_D2 These are the conduction losses of IGBT 1, diode 1, IGBT 2, and diode 2, respectively.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. The proposed method for estimating the capacitor voltage of a multilevel energy storage converter submodule based on junction temperature monitoring in this invention estimates the capacitor voltage in the submodule by monitoring the junction temperature and case temperature of the power devices in each bridge arm submodule and utilizing the mathematical relationship between the junction temperature difference and the capacitor voltage of the submodule. This method does not increase the hardware cost or software complexity of the modular multilevel energy storage converter sensor, has little impact on the output power quality of the modular multilevel energy storage converter, and is simple and easy to implement.

[0030] 2. The capacitor voltage estimation method for multilevel energy storage converter submodules based on junction temperature monitoring proposed in this invention only needs to estimate the capacitor voltage based on the junction temperature and case temperature obtained by real-time monitoring of the system. It does not require changing the topology of the modular multilevel energy storage converter submodule, does not increase the hardware cost of the modular multilevel energy storage converter, and is easy to implement in existing modular multilevel energy storage converters, thus having strong practicality.

[0031] 3. The multilevel energy storage converter submodule capacitor voltage estimation method proposed in this invention based on junction temperature monitoring can achieve the estimation of the capacitor voltage of the modular multilevel energy storage converter submodule without increasing the hardware and software implementation costs. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the modular multilevel energy storage converter topology according to an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the submodule topology of an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the overall method flow of an embodiment of the present invention. Detailed Implementation

[0035] Multilevel energy storage converter submodule, the topology of which is as follows: Figure 1-2 As shown, the multilevel energy storage converter consists of six bridge arms, each of which includes n sub-modules SM with identical topologies connected in series, and one bridge arm inductor L. s The bridge arm resistor R; the submodule SM is a half-bridge structure, consisting of two diodes D1 and D2, two IGBT power switches T1 and T2, and a DC capacitor C. i The diodes D1 and D2 are connected in reverse parallel to the switching terminals of IGBT power switches T1 and T2, respectively. The controlled terminals of IGBT power switches T1 and T2 are connected to signal S. j_k_i The input signal i at the series connection point of IGBT power switches T1 and T2 jk The two external terminals are connected through capacitor C. i connect.

[0036] like Figure 3 As shown, based on the above system, the specific steps of the method for estimating the capacitor voltage of a multi-level energy storage converter submodule are as follows:

[0037] S1. Real-time monitoring of the junction temperature T of power devices in each submodule. jun_j_k_i_g (j=a,b,c;k=u,l;i=1,2,…,n;g=T1,D1;T2,D2), the shell temperature T of each submodule within the bridge arm h_j_k_i The current i in each bridge arm jk Switching signals S of submodules within each bridge arm j_k_i As shown in the figure, a, b, and c are the connection points of the three phases, and u and l are the upper and lower bridge arms of the multi-level energy storage converter, respectively.

[0038] S2. Utilize the monitored junction temperature T of the power devices in the submodule. jun_j_k_i_g , Submodule's shell temperature T h_j_k_i The thermal resistance parameter R of the IGBT in the power device datasheet th_jh_T The thermal resistance parameter R of the diode th_jh_D Obtain the power loss P of the power devices in the submodule loss_j_k_i_g ;

[0039] Specifically, this includes the power loss P of IGBT No. 1. loss_j_k_i_T1 Power loss P of diode #1 loss_j_k_i_D1 Power loss P of IGBT No. 2loss_j_k_i_T2 and the power loss P of diode 1 loss_j_k_i_D2 The calculation formula is as follows:

[0040]

[0041] In the formula T jun_j_k_i_T1 T jun_j_k_i_D1 T jun_j_k_i_T2 T jun_j_k_i_T2 This refers to the junction temperature of IGBT 1, diode 1, IGBT 2, and diode 2 in the submodule.

[0042] S3. Utilize the monitored current i of each bridge arm jk The switching signals S of the submodules within each bridge arm j_k_i The on-state voltage drop V of the IGBT in the power device datasheet ce0 Diode forward voltage drop V d0 IGBT on-state resistance R ce Diode on-resistance R d The conduction loss P of each power device in the submodule is obtained. con_j_k_i_g and switching frequency f sw_g ;

[0043] Specifically, this includes the switching frequency f of IGBT No. 1 in the submodule. sw_T1 The switching frequency f of diode #1 sw_D1 The switching frequency f of IGBT No. 2 sw_T2 and the switching frequency f of diode #2 sw_D1 The calculation formula is as follows:

[0044]

[0045] In the formula, T is the fundamental frequency period of the converter operation.

[0046] Using the monitored current i of each bridge arm jk The switching signals S of the submodules within each bridge arm j_k_i The switching loss energy E of the power devices in each submodule is obtained by comparing the switching loss characteristic curves of the power devices in the datasheets of each bridge arm submodule. sw_j_k_i_g ;

[0047] Specifically, this includes the energy loss E of the No. 1 IGBT switch. sw_j_k_i_T1 Energy loss E of diode #1 sw_j_k_i_D1 Energy loss E of IGBT No. 2 sw_j_k_i_T2 And the switching loss energy E of diode No. 2 sw_j_k_i_D2 The calculation formula is:

[0048]

[0049] In the formula p sw_j_k_i_T1 p sw_j_k_i_D1 p sw_j_k_i_T2 p sw_j_k_i_D2 These represent the instantaneous switching energy of IGBT 1, diode 1, IGBT 2, and diode 2, respectively.

[0050] S4. Utilize the power loss P of each power device loss_j_k_i_g The switching frequency f of each power device sw_g Switching loss energy E of each power device sw_j_k_i_g The test voltage V in the power device datasheet ref_test Finally, the capacitor voltage V in each submodule is obtained. sm_j_k_i The calculation method is as follows:

[0051]

[0052] In the formula V sm_j_k_i_0 V sm_j_k_i_1 V sm_j_k_i_2 V sm_j_k_i_3 These are the values ​​of the submodule capacitor voltage at time 0, T / 4, 2T / 4, and 3T / 4 of the fundamental period, respectively; P con_j_k_i_T1 P con_j_k_i_D1 P con_j_k_i_T2 P con_j_k_i_D2 These are the conduction losses of IGBT 1, diode 1, IGBT 2, and diode 2, respectively.

[0053] This invention monitors the junction and case temperatures of each submodule, then calculates the power device losses based on the relationship between temperature and thermal resistance. Finally, it estimates the submodule capacitor voltage in a modular multilevel energy storage converter based on the mathematical relationship between losses and submodule capacitor voltage. The algorithm is simple and easy to implement. Furthermore, this invention does not require changes to the topology of the modular multilevel energy storage converter submodules, does not increase the hardware cost of the modular multilevel energy storage converter, and is easily implemented in existing modular multilevel energy storage converters, making it highly practical.

[0054] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for estimating the capacitor voltage of a multilevel energy storage converter submodule, characterized in that, A multilevel energy storage converter submodule, wherein the multilevel energy storage converter includes six bridge arms, characterized in that each bridge arm includes n submodules SM with the same topology connected in series, a bridge arm inductor Ls, and a bridge arm resistor R; Submodule SM is a half-bridge structure, consisting of two diodes D1 and D2, two IGBT power switches T1 and T2, and a DC capacitor Ci. Diodes D1 and D2 are connected in reverse parallel to the switching terminals of IGBT power switches T1 and T2, respectively. The controlled terminals of IGBT power switches T1 and T2 are connected to signal S. j_k_i The input signal i at the series connection point of IGBT power switches T1 and T2 jk The two external terminals are connected via capacitor Ci; The capacitor voltage estimation method includes the following steps: S1. Real-time monitoring of the junction temperature T of power devices in each submodule. jun_j_k_i_g Where j=a,b,c; k=u,l; i=1,2,…,n; g=T1,D1,T2,D2; and the shell temperature T of each submodule within the bridge arm. h_j_k_i The current i in each bridge arm jk Switching signals S of submodules within each bridge arm j_k_i a, b, c are the connection points of the three phases, and u, l are the upper and lower bridge arms of the multi-level energy storage converter, respectively. S2. Utilize the monitored junction temperature T of the power devices in the submodule. jun_j_k_i_g , Submodule's shell temperature T h_j_k_i The thermal resistance parameter R of the IGBT in the power device datasheet th_jh_T The thermal resistance parameter R of the diode th_jh_D Obtain the power loss P of the power devices in the submodule loss_j_k_i_g ; S3. Utilize the monitored current i of each bridge arm jk The switching signals S of the submodules within each bridge arm j_k_i The on-state voltage drop V of the IGBT in the power device datasheet ce0 Diode forward voltage drop V d0 IGBT on-state resistance R ce Diode on-resistance R d The conduction loss P of each power device in the submodule is obtained. con_j_k_i_g and switching frequency f sw_g ; Using the monitored current i of each bridge arm jk The switching signals S of the submodules within each bridge arm j_k_i The switching loss energy E of the power devices in each submodule is obtained by comparing the switching loss characteristic curves of the power devices in the datasheets of each bridge arm submodule. sw_j_k_i_g ; S4. Utilize the power loss P of each power device loss_j_k_i_g The switching frequency f of each power device sw_g Switching loss energy E of each power device sw_j_k_i_g The test voltage V in the power device datasheet ref_test Finally, the capacitor voltage V in each submodule is obtained. sm_ j_k_i .

2. The method for estimating the capacitor voltage of a multi-level energy storage converter submodule according to claim 1, characterized in that, Step S2 specifically includes: power loss P of IGBT No. 1 loss_j_k_i_T1 Power loss P of diode #1 loss_j_k_i_D1 Power loss P of IGBT No. 2 loss_j_k_i_T2 and the power loss P of diode 1 loss_j_k_i_D2 The calculation formula is as follows: (1) In the formula T jun_j_k_i_T1 T jun_j_k_i_D1 T jun_j_k_i_T2 T jun_j_k_i_T2 This refers to the junction temperature of IGBT 1, diode 1, IGBT 2, and diode 2 in the submodule.

3. The method for estimating the capacitor voltage of a multi-level energy storage converter submodule according to claim 2, characterized in that, In step S3, the switching frequency f sw_g The calculation steps are as follows: Specifically, this includes the switching frequency f of IGBT No. 1 in the submodule. sw_T1 The switching frequency f of diode #1 sw_D1 The switching frequency f of IGBT No. 2 sw_T2 and the switching frequency f of diode #2 sw_D1 The calculation formula is as follows: (2) In the formula, T is the fundamental frequency period of the converter operation.

4. The method for estimating the capacitor voltage of a multi-level energy storage converter submodule according to claim 3, characterized in that, Switching loss energy E of power devices in submodule sw_j_k_i_g Specifically, this includes the energy loss E of the No. 1 IGBT switch. sw_j_k_i_T1 Energy loss E of diode #1 sw_j_k_i_D1 Energy loss of IGBT No. 2 switch E sw_j_k_i_T2 And the switching loss energy E of diode No. 2 sw_j_k_i_D2 The calculation formula is: (3) In the formula p sw_j_k_i_T1 p sw_j_k_i_D1 p sw_j_k_i_T2 p sw_j_k_i_D2 These represent the instantaneous switching energy of IGBT 1, diode 1, IGBT 2, and diode 2, respectively.

5. The method for estimating the capacitor voltage of a multi-level energy storage converter submodule according to claim 4, characterized in that, Step S4: Capacitor voltage V in each submodule sm_ j_k_i The calculation method is as follows: (4) In the formula V sm_ j_k_i_0 V sm_ j_k_i_1 V sm_ j_k_i_2 V sm_ j_k_i_3 These are the values ​​of the submodule capacitor voltage at time 0, T / 4, 2T / 4, and 3T / 4 of the fundamental period, respectively; P con_j_k_i_T1 P con_j_k_i_D1 P con_j_k_i_T2 P con_j_k_i_D2 These are the conduction losses of IGBT 1, diode 1, IGBT 2, and diode 2, respectively.

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